,1.00 



Figure 127 - Profile of U.S. Navy Strut 



No. 2 (pointed) and closely similar 



Joukowski profile (rounded), with 



theoretical and experimental 



pressure distributions. See 



the end of Sec. 79. 



I — Joukowski 

 , — Sources and Sinks 

 -Experimental 



Figure 128 - Flow without circulation past 

 a similar profile with rounded ends. 



80. IMPROVED AIRFOILS 



A modification of the Joukowski transformation by which the sides of the airfoil may 

 be made to form a trailing edge containing a finite angle instead of a cusp is furnished by the 

 circular-arc transformation, which will be treated in Section 88. There is no simple graphical 

 construction for this transformation. It was studied by von Karman and Trefftz , MiTllor , 

 and Glauert^^"*, and was generalized further by Betz and Keune''^, who added a dipole term. 



Other closed transformations for the construction of airfoil contours were discussed by 

 Elasius^°, riercy, Fiper and Preston^\ Fiper^^, and Burington and Dobbie^^, More 

 generally, any ordinary closed curve can be transformed into a circle by a suitable trans- 

 formation; in order to make the two planes agree at infinity, the transformation must be repre- 

 sentable by a Laurent series of the form mentioned in Section 76 or 



The use of transformations so defined was studied by von Mises^'' and by fiiller^^. 



189 



